JP6249228B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte secondary battery.

Nonaqueous electrolyte secondary batteries such as lithium ion secondary batteries are preferably used for so-called portable power supplies, high-output power supplies for vehicles, and the like because they are lighter and have higher energy density than existing batteries.
In such a non-aqueous electrolyte secondary battery, higher power density is being studied as part of performance improvement. Such high power density can be realized by adjusting the properties of the positive electrode active material, for example. For example, Patent Document 1 includes a positive electrode active material having a BET specific surface area of 0.5 to 1.9 m ² / g and / or a DBP absorption of 20 mL / 100 g or more, so that the internal resistance is low and the output characteristics are improved. It is described that an excellent secondary battery can be realized.

JP 2012-109166 A

By the way, the non-aqueous electrolyte secondary battery may be in an overcharged state and the battery temperature may rise when a current higher than normal is supplied due to an erroneous operation or the like. In recent years, from the viewpoint of improving reliability, there has been a demand for stably and further suppressing the increase in battery temperature during overcharging (more excellent overcharge resistance). Preferably, it is desired that the overcharge resistance and the original characteristics of the battery (for example, high output density and high energy density) are compatible at a high level.
The present invention has been made in view of such circumstances, and the object thereof is a non-aqueous electrolyte secondary solution excellent in overcharge resistance performance (preferably having high overcharge resistance performance and excellent battery characteristics). To provide a battery.

The present inventors have studied from various angles and have come to the conclusion that it is important to control the surface area of the positive electrode active material (specifically, the BET specific surface area and the DBP absorption amount) in order to solve the above problems. It was. That is, for example, when the BET specific surface area of the positive electrode active material is increased, the reaction field between the positive electrode active material and the charge carrier is increased, which may lead to improvement of battery characteristics (for example, energy density). However, on the other hand, the reaction field on the positive electrode may increase during overcharging, resulting in a large amount of heat generation.
Therefore, as a result of intensive studies to achieve both these conflicting characteristics at a high level, the present invention has been created.

The non-aqueous electrolyte secondary battery disclosed herein includes a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and a non-aqueous electrolyte. Then, when the BET specific surface area (m ² / g) of the positive electrode active material is S and the DBP absorption amount (ml / 100 g) is Q, the BET specific surface area and the DBP absorption amount are two-dimensional. In the coordinate system of (5), the above (S, Q) has the following five coordinate points: (0.1, 30), (0.95, 30), (1.7, 37.5), (1.7). , 71), (0.1, 54); are in the range of a pentagon formed by connecting the adjacent coordinate points linearly.
By setting the BET specific surface area S and the DBP absorption amount Q of the positive electrode active material within the above ranges, high overcharge resistance can be stably realized. And preferably, the non-aqueous-electrolyte secondary battery which has high overcharge-proof performance and the outstanding battery characteristic is realizable.

In the present specification, “BET specific surface area” refers to a specific surface area obtained by analyzing a surface area measured by a constant volume adsorption method using nitrogen gas by a BET method (for example, a BET multipoint method).
Specifically, first, about 0.5 g of a sample is put into a measurement cell and dried (pretreatment) at 100 ° C. for 3 hours. Next, the above sample was measured at 8 points in the range of relative pressure 0.025 to 0.200 using a general specific surface area measuring device (for example, Autosorb 1 manufactured by Quantachrome Instruments), and the result was obtained. It refers to the specific surface area obtained by analyzing by the BET method.
In this specification, “DBP absorption” refers to a general absorption measurement device (for example, absorption measurement device S410 from Asahi Research Institute), and DBP (dibutyl phthalate) is used as a reagent liquid. The value measured in accordance with JIS K6217-4 (2008) “Carbon black for rubber—Basic characteristics—Part 4: Determination of DBP absorption”.

It is a graph which shows the relationship between the BET specific surface area of a positive electrode active material, and DBP absorption.

  Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than matters specifically mentioned in the present specification (for example, the properties of the positive electrode active material) and matters necessary for the implementation of the present invention (for example, battery components and general features that do not characterize the present invention) Can be understood as a design matter of a person skilled in the art based on the prior art in the field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

≪Nonaqueous electrolyte secondary battery≫
The non-aqueous electrolyte secondary battery disclosed herein includes a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and a non-aqueous electrolyte. And the characteristic of a positive electrode active material is characterized by satisfy | filling a predetermined requirement. Therefore, the other components are not particularly limited, and can be arbitrarily determined according to various uses. Hereinafter, each component will be described in order.

  The positive electrode of the nonaqueous electrolyte secondary battery disclosed herein includes at least a positive electrode active material. As such a positive electrode, a positive electrode active material powder (particles) is preferably fixed on a positive electrode current collector together with a binder, a conductive material and the like to form a positive electrode active material layer. As the positive electrode current collector, a conductive member made of a highly conductive metal (for example, aluminum, nickel, etc.) is suitable.

In the technology disclosed herein, the BET specific surface area S (m ² / g) and the DBP absorption amount Q (ml / 100 g) of the positive electrode active material are controlled to be within a predetermined range. Specifically, as shown in FIG. 1, in a two-dimensional (planar) XY coordinate system in which the BET specific surface area is the vertical axis (Y axis) and the DBP absorption amount is the horizontal axis (X axis), the following 5 Two coordinate points: (0.1,30), (0.95,30), (1.7,37.5), (1.7,71), (0.1,54); adjacent coordinates The properties of the positive electrode active material are controlled so that (S, Q) falls within the pentagonal range obtained by connecting the points in a straight line.

In other words, when the BET specific surface area S (m ² / g) and the DBP absorption amount Q (ml / 100 g) of the positive electrode active material are outside the pentagonal range shown in FIG. May deteriorate the anti-overcharge performance). Specifically, the following problems may occur.
In region A (that is, a region where the amount of DBP absorption of the positive electrode active material is less than 30), the positive electrode active material and the non-aqueous electrolyte solution are difficult to get into, and the impregnation of the non-aqueous electrolyte solution does not proceed to the inside of the positive electrode May occur.
In region B (that is, the region where the BET specific surface area of the positive electrode active material exceeds 1.7 m ² / g), the surface area of the positive electrode active material is too large, and the reaction field on the surface of the positive electrode during overcharging increases. Heat generation may increase.
In region C, it may be difficult to produce a positive electrode (typically a positive electrode active material layer) because the BET specific surface area of the positive electrode active material is too large and / or the DBP absorption amount is too high. .
In region D (that is, a region where the BET specific surface area of the positive electrode active material is less than 0.1 m ² / g), the particle size of the positive electrode active material is too large, and thus the firing during the production of the active material is non-uniform Thus, it may be difficult to produce a homogeneous positive electrode (typically, a positive electrode active material layer).
In region E, since the DBP absorption amount is small with respect to the BET specific surface area of the positive electrode active material, the positive electrode undecomposed portion remains during overcharging, and battery heat generation may increase. That is, the non-aqueous electrolyte does not impregnate the inside of the positive electrode, and the decomposition reaction does not proceed uniformly inside the positive electrode during overcharge, so the inside of the positive electrode (typically relatively far from the surface of the positive electrode active material) An undecomposed portion may remain in a region (for example, a region near the positive electrode current collector), which may increase battery heat generation during overcharge.
The technique disclosed here avoids the occurrence of the above-described problems by controlling the surface area (BET specific surface area and DBP absorption amount) of the positive electrode active material within the above pentagonal range, and has high reliability ( Typically, it achieves overcharge resistance). Furthermore, excellent battery characteristics such as high energy density and high power density can be realized.

As the positive electrode active material, a layered lithium transition metal composite oxide material (for example, LiCoO ₂ , LiNiO ₂ , LiNi _0.33 Mn _0.33 Co _0.33 O ₂ or the like) is preferable. Of these, lithium nickel manganese cobalt based composite oxide is preferable from the viewpoint of energy density and thermal stability. The BET specific surface area of the positive electrode active material is not particularly limited as long as the surface area property is satisfied, but is more preferably 0.5 to 1.5 m ² / g. The DBP absorption amount of the positive electrode active material is not particularly limited as long as the surface area property is satisfied, but it is more preferably 35 to 54 ml / 100 g. By satisfying at least one of these, a non-aqueous electrolyte secondary battery with higher overcharge resistance can be realized more stably.

  As the binder, a vinyl halide resin such as polyvinylidene fluoride (PVdF) or a polyalkylene oxide such as polyethylene oxide (PEO) is suitable. As the conductive material, carbon materials such as carbon black (typically acetylene black and ketjen black) and activated carbon are suitable.

  The proportion of the positive electrode active material in the entire positive electrode active material layer is suitably about 50% by mass or more from the viewpoint of improving energy density, and is usually 50 to 98% by mass, for example, 80 to 95% by mass. Good. The proportion of the binder in the entire positive electrode active material layer is suitably about 0.5 to 10% by mass, for example, from the viewpoint of improving mechanical strength and durability, and is usually about 1 to 5% by mass. Good. The proportion of the conductive material in the entire positive electrode active material layer is suitably about 0 to 15% by mass from the viewpoint of improving the output density and reducing the resistance, and is usually about 1 to 10% by mass.

  The negative electrode of the nonaqueous electrolyte secondary battery disclosed herein includes at least a negative electrode active material. As such a negative electrode, a negative electrode active material powder (particles) is preferably fixed on a negative electrode current collector together with a binder, a thickener and the like to form a negative electrode active material layer. As the negative electrode current collector, a conductive material made of a metal having good conductivity (for example, copper, nickel, etc.) is suitable. As the negative electrode active material, carbon materials such as graphite (graphite), non-graphitizable carbon (hard carbon), graphitizable carbon (soft carbon) and the like are preferable, and graphite is particularly preferable from the viewpoint of energy density and durability. . As the binder, styrene butadiene rubber (SBR), polytetrafluoroethylene (PTFE) and the like are suitable. As the thickener, a carboxymethyl cellulose (CMC) cellulosic material is suitable. As the negative electrode current collector, a conductive material made of a highly conductive metal (for example, copper) is suitable.

  The positive electrode and the negative electrode of the non-aqueous electrolyte secondary battery disclosed herein typically face each other with a separator interposed therebetween. As the separator, a porous resin sheet made of a resin such as polyethylene (PE) or polypropylene (PP) is suitable. A porous heat-resistant layer may be provided on one side or both sides of the porous resin sheet.

The non-aqueous electrolyte solution of the non-aqueous electrolyte secondary battery disclosed herein typically exhibits a liquid state at normal temperature (for example, 25 ° C.), and is preferably always liquid within the operating temperature range (for example, −20 to 60 ° C.). Presents. As the nonaqueous electrolytic solution, a nonaqueous solvent containing a supporting salt (for example, a lithium salt in a lithium ion secondary battery) can be suitably used.
As the non-aqueous solvent, aprotic solvents such as carbonates, esters, ethers, nitriles, sulfones and lactones are suitable. Of these, carbonates such as ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) are preferable from the viewpoint of durability. As the supporting salt, a lithium salt, a sodium salt, a magnesium salt, and the like are preferable, and lithium salts such as LiPF ₆ and LiBF ₄ are particularly preferable.

≪Use of non-aqueous electrolyte secondary battery≫
The non-aqueous electrolyte secondary battery disclosed herein stably realizes higher reliability (overcharge resistance) than conventional products due to the effect of controlling the properties (surface area) of the positive electrode active material. To get. Preferably, high energy density, high power density, and high reliability can be combined. Therefore, such a non-aqueous electrolyte secondary battery can be used for various applications, but it can be preferably used in applications that require high energy density, high input / output density, and high reliability by taking advantage of such characteristics. it can. Examples of such applications include drive power supplies mounted on vehicles such as plug-in hybrid vehicles, hybrid vehicles, and electric vehicles.

  Hereinafter, some examples relating to the present invention will be described. However, the present invention is not intended to be limited to the specific examples.

<Construction of lithium ion secondary battery>
As the positive electrode active material, lithium nickel manganese cobaltate (Li (Ni _0.33 Mn _0.33 Co _0.33 ) O ₂ ) having a surface area property shown in Table 1 was prepared. By mixing the positive electrode active material, acetylene black (AB) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder, and adjusting the viscosity with N-methylpyrrolidone (NMP), the positive electrode active material layer A forming slurry was prepared. The slurry was applied to the surface of an aluminum foil (positive electrode current collector) and dried to form a positive electrode active material layer. After rolling this, slit processing to a predetermined size is performed to obtain sheet-like positive electrodes (Examples 1 to 9 and Comparative Examples 1 to 3) having a positive electrode active material layer on the positive electrode current collector. It was.

Next, carbon as a negative electrode active material, styrene butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener are mixed, and the viscosity is adjusted with ion-exchanged water, whereby the negative electrode active material is adjusted. A slurry for forming a material layer was prepared. The slurry was applied to the surface of a copper foil (negative electrode current collector) and dried to form a negative electrode active material layer. This was roll-rolled and then slitted to a predetermined size to obtain a sheet-like negative electrode having a negative electrode active material layer on the negative electrode current collector.
The produced sheet-like positive electrode and negative electrode were laminated via a separator sheet to produce electrode bodies (Examples 1 to 9, Comparative Examples 1 to 3). As the separator, a porous sheet having a three-layer structure made of polypropylene (PP) / polyethylene (PE) / polypropylene (PP) was used.

Next, this electrode body was accommodated in a rectangular battery case made of aluminum, and a non-aqueous electrolyte was injected. As the non-aqueous electrolyte, a mixed solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) at a volume ratio of 3: 4: 3, and LiPF ₆ as a supporting salt is used. What was melt | dissolved in the density | concentration of about 1 mol / L was used. The opening of the battery case is sealed, and a thermocouple is attached to the outer surface of the battery case to construct lithium ion secondary batteries (theoretical capacity 3.8 Ah) of Examples 1 to 9 and Comparative Examples 1 to 3. did.

<Overcharge test>
The battery thus constructed was subjected to a conditioning treatment, and then the initial capacity was confirmed in a voltage range of 3.0 to 4.2 V to confirm that there was no abnormality. Next, this battery was charged with a constant current of 10 A until the overcharged state with an upper limit voltage of 10 V under a temperature environment of 25 ° C., and the maximum battery temperature (° C.) at this time was confirmed. The results are shown in Table 1.

As is clear from Table 1, in Examples 1 to 9, the maximum battery temperature during overcharging is lower than in Comparative Examples 1 to 3, and specifically, the maximum battery temperature is 140 ° C. or lower (eg, 130 ° C. or lower). It was suppressed to. This is presumably because the non-aqueous electrolyte could be sufficiently penetrated into the positive electrode by controlling the BET specific surface area and the DBP absorption amount of the positive electrode active material. As a result, it is presumed that the inside of the positive electrode can be reacted uniformly during overcharging, and the heat generation of the positive electrode can be suppressed low. In particular, when the positive electrode active material has a DBP absorption of 35 ml / 100 g or more (for example, 40 ml / 100 g or more) and satisfies 54 ml / 100 g or less, it has been found that higher overcharge resistance can be realized. . Further, it was found that when the positive electrode active material has a BET specific surface area of 1.5 m ² / g or less (for example, 1.0 m ² / g or less), higher overcharge resistance can be realized. These results show the technical significance of the present invention.

  As mentioned above, although this invention was demonstrated in detail, the said embodiment and Example are only illustrations and what changed and modified the above-mentioned specific example is included in the invention disclosed here.

Claims (2)

A non-aqueous electrolyte secondary battery comprising a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and a non-aqueous electrolyte,
The positive electrode active material is a layered lithium transition metal composite oxide,
When the BET specific surface area (m ² / g) of the positive electrode active material is S and the DBP absorption amount (ml / 100 g) is Q,
In the two-dimensional coordinate system using the BET specific surface area and the DBP absorption amount as variables, the (S, Q) is represented by the following coordinate points: (0.95, 30), (1.7, 37.5) , (1.7,71); in the range formed by connecting straight at the coordinate point adjacent the, and wherein S is characterized der Rukoto least 1.6 m ² / g, the non Water electrolyte secondary battery. S is 1.6m ² The non-aqueous electrolyte secondary battery according to claim 1, which is / g.

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